Patent GB-459807-A (GB)
Title: Improvements in or relating to overload circuit breakers
IPC: H01H71/40
Filed: 1935-09-27
Abstract: 459,807. Electrically-tripped switches. CRABTREE, G. E., Endwood, Little Aston Park, Sutton Coldfield, ELLIOTT, W. T., The Vicarage, Grosvenor Mount, Leeds, BADHAM, E., 34, Buchanan Road, Walsall, and THORNTON, R. W., 3, King Edward Street, Oxford, [Representatives of CRABTREE, J. A.].-(Schiele & Bruchsaler Industriewerke Akt.-Ges. ; Baden-Baden, Germany) Sept. 27, 1935, No. 26700. [Class 38 (v)] Trip-mechanism for circuit-breakers, of the kind in which a thermal element is adapted, on overload, so to displace the armature of an electromagnet that the armature is attracted to the magnet to actuate the trip-mechanism, comprises an electromagnet or electromagnets so arranged that under normal loads opposed and balanced forces act on opposite sides or ends of a pivoted armature, and a thermal element which, on overload, undergoes a predetermined change in form and disturbs the equilibrium of the forces acting in the armature. In one construction, Fig. 3, a heating-coil 2 surrounding a bimetallic strip 3 is connected in series with a winding 1a on the centre limb of an E-shaped core 1. The armature 4 is supported on a knife-edge pivot 5 mounted on the centre limb of the core, and its ends are normally equally attracted by the two side limbs of the core. An adjustable stop 8 prevents movement of the armature in a counter-clockwise direction. When the strip 2 bends towards the right, it engages an extension 4a of the armature and moves the latter in a clockwise direction. The balance of the magnetic forces acting on the armature is thereby upset, and the righthand end of the armature is attracted by the corresponding pole of the electromagnet and releases the catch 6. In a modification, Fig. 4 (not shown), separate electromagnets on opposite sides of one end of the armature exert balanced forces on the latter until the armature is moved towards one of the magnets by the bending of the bimetallic strip. In another construction, Fig. 5 (not shown) a single electromagnet with a longitudinal core is provided, each end of the core carrying a plate having two polepieces, one on each side of the armature. In the construction shown in Fig. 6, electromagnets 1<1>, 1<11> are arranged on opposite sides of the armature 4, the windings 1a<1>, 1a<11> of the electromagnets being in series with the heating coil 2, and the secondary winding 9 of a transformer. When the strip 3 bends, the winding 1a<1> is short-circuited and the armature is attracted by the electromagnet 111 to release the catch 6. In a modification, the windings of the electromagnet are in parallel, one of them being adapted to be short-circuited by the bending of the bimetallic strip. In another construction, Fig. 8 (not shown), the armature is carried by the bimetallic strip, which is mounted on a member rotatable against the action of a spring. In the construction shown in Fig. 9, the electromagnet 1 has four polepieces, only two of which are seen, and two exciting coils 1a<1> and 1a<11>, of which the latter exerts a force in the releasing direction on the armature 4, while the coil 1a<1> exerts an opposing force. The heating coil 2 of the bimetallic strip 3 is included in the circuit of the coil 1a<1>. When the strip bends to the right, a latch between the strip and armature is released, and the armature is given an initial movement in the releasing direction, which movement is completed by the magnetic force due to the coil 1a<11>. The armature strikes the extension 6 of the release shaft 6a and the circuit is opened at the contacts 11, 12, the electromagnet 1 generating a blowout field for the arc. In another construction, Fig. 10, the armature 4 is in two parts 4a, 4b, held together by a spring 13, the tension of which is adjusted by a nut 14. Under comparatively low overloads, the bimetallic strip 3 tilts the armature in a counterclockwise direction to upset the balance of the magnetic forces as in the preceding constructions, but on heavy overloads, the part 4a of the armature is attracted by the corresponding pole of the magnet 1 against the action of the spring 13, and the switch is released. The heating- coil 3 is in series with a secondary winding 1b of the electromagnet. In another construction, Fig. 11 (not shown), the electromagnet has an E-shaped core with an exciting winding on the centre limb and secondary windings on the outer limbs in series with the heating coil, one of the secondary windings being adapted to be short-circuited by the bending of the bimetallic strip.